Integrated circuit including u-shaped access device

ABSTRACT

An integrated circuit includes a first contact, a second contact, and a U-shaped access device coupled to the first contact and the second contact. The integrated circuit includes self-aligned dielectric material isolating the first contact from the second contact.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to U.S. patent application Ser. No. ______, Attorney Docket Number Q600.128.101, entitled “INTEGRATED CIRCUIT INCLUDING U-SHAPED ACCESS DEVICE,” filed on the same date as the present application, which is incorporated herein by reference.

BACKGROUND

One type of memory is resistive memory. Resistive memory utilizes the resistance value of a memory element to store one or more bits of data. For example, a memory element programmed to have a high resistance value may represent a logic “1” data bit value and a memory element programmed to have a low resistance value may represent a logic “0” data bit value. Typically, the resistance value of the memory element is switched electrically by applying a voltage pulse or a pattern of voltage pulses or a current pulse or a pattern of current pulses to the memory element.

One type of resistive memory is phase change memory. Phase change memory uses a phase change material in the resistive memory element. The phase change material exhibits at least two different states. The states of the phase change material may be referred to as the amorphous state and the crystalline state, where the amorphous state involves a more disordered atomic structure and the crystalline state involves a more ordered lattice. The amorphous state usually exhibits higher resistivity than the crystalline state. Also, some phase change materials exhibit multiple crystalline states, e.g. a face-centered cubic (FCC) state and a hexagonal closest packing (HCP) state, which have different resistivities and may be used to store bits of data. In the following description, the amorphous state generally refers to the state having the higher resistivity and the crystalline state generally refers to the state having the lower resistivity.

Phase changes in the phase change materials may be induced reversibly. In this way, the memory may change from the amorphous state to the crystalline state—“set”—and from the crystalline state to the amorphous state—“reset”—in response to temperature changes. The temperature changes of the phase change material may be achieved by driving current through the phase change material itself or by driving current through a resistive heater adjacent the phase change material. With both of these methods, controllable heating of the phase change material causes controllable phase change within the phase change material.

A phase change memory including a memory array having a plurality of memory cells that are made of phase change material may be programmed to store data utilizing the memory states of the phase change material. One way to read and write data in such a phase change memory device is to control a current and/or a voltage pulse or a pattern of pulses that is applied to the phase change material. The temperature in the phase change material in each memory cell generally corresponds to the applied level of current and/or voltage to achieve the heating.

To achieve higher density phase change memories, a phase change memory cell can store multiple bits of data. Multi-bit storage in a phase change memory cell can be achieved by programming the phase change material to have intermediate resistance values or states, where the multi-bit or multilevel phase change memory cell can be written to more than two states. If the phase change memory cell is programmed to one of three different resistance levels, 1.5 bits of data per cell can be stored. If the phase change memory cell is programmed to one of four different resistance levels, two bits of data per cell can be stored, and so on. To program a phase change memory cell to an intermediate resistance value, the amount of crystalline material coexisting with amorphous material and hence the cell resistance is controlled via a suitable write strategy.

Higher density phase change memories can also be achieved by reducing the physical size of each memory cell. Increasing the density of a phase change memory increases the amount of data that can be stored within the memory while at the same time typically reducing the cost of the memory. A relatively high current is used to reset a phase change memory cell. The access device used to access a phase change memory cell has to be capable of providing the high current. The high current can most efficiently (i.e., with the smallest memory cell size) be provided by a bipolar device such as a diode. Diodes are typically fabricated after transistor formation using a selective epitaxy process, which requires an ultra-high vacuum chemical vapor deposition (UHV-CVD) tool to meet the temperature budget requirements.

For these and other reasons, there is a need for the present invention.

SUMMARY

One embodiment provides an integrated circuit. The integrated circuit includes a first contact, a second contact, and a U-shaped access device coupled to the first contact and the second contact. The integrated circuit includes self-aligned dielectric material isolating the first contact from the second contact.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of embodiments and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and together with the description serve to explain principles of embodiments. Other embodiments and many of the intended advantages of embodiments will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.

FIG. 1 is a block diagram illustrating one embodiment of a system.

FIG. 2 is a diagram illustrating one embodiment of a memory device.

FIG. 3 illustrates a cross-sectional view of one embodiment of a U-shaped diode access device.

FIG. 4 illustrates a cross-sectional view of one embodiment of a bipolar transistor access device.

FIG. 5 illustrates a cross-sectional view of one embodiment of an array of diode access devices.

FIG. 6 illustrates a cross-sectional view of another embodiment of an array of diode access devices.

FIG. 7 illustrates a cross-sectional view of one embodiment of an array of bipolar transistor access devices.

FIG. 8 illustrates a cross-sectional view of another embodiment of an array of bipolar transistor access devices.

FIG. 9A illustrates a top view of one embodiment of a substrate.

FIG. 9B illustrates a cross-sectional view of one embodiment of the substrate.

FIG. 9C illustrates another cross-sectional view of one embodiment of the substrate perpendicular to the view illustrated in FIG. 9B.

FIG. 10A illustrates a cross-sectional view of one embodiment of the substrate after doping.

FIG. 10B illustrates a cross-sectional view of one embodiment of the substrate after doping including optional co-implants.

FIG. 11 illustrates a cross-sectional view of one embodiment of the substrate, a doped polysilicon layer, a word line material layer, and a nitride layer.

FIG. 12 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layer, word lines, and the nitride layer after etching.

FIG. 13 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layer, the word lines, and an optional nitride layer.

FIG. 14 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layer, the word lines, the nitride layer, and a polysilicon layer.

FIG. 15 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layer, the word lines, the nitride layer, the polysilicon layer, and an oxide layer.

FIG. 16 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layer, the word lines, the nitride layer, a polysilicon layer, and the oxide layer after etching.

FIG. 17 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layer, the word lines, the nitride layer, the polysilicon layer, and the oxide layer after oxidation.

FIG. 18 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layer, the word lines, the nitride layer, the polysilicon layer, and oxide.

FIG. 19 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layer, the word lines, the nitride layer, the oxide, and a doped polysilicon layer.

FIG. 20 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layers, the word lines, the nitride layer, and the oxide after annealing.

FIG. 21 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layers, the word lines, the nitride layer, the oxide, and a contact material layer.

FIG. 22 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layers, the word lines, a nitride layer, the oxide, the contact material layer, and a bottom electrode material layer.

FIG. 23A illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layers, the word lines, a nitride layer, the oxide, the contact material layer, the bottom electrode material layer, a phase change material layer, and a top electrode material layer.

FIG. 23B illustrates another cross-sectional view of one embodiment of the substrate, the doped polysilicon layers, the word lines, the nitride layer, the oxide, the contact material layer, the bottom electrode material layer, the phase change material layer, and the top electrode material layer.

FIG. 23C illustrates another cross-sectional view of one embodiment of the substrate, the doped polysilicon layers, the word lines, the nitride layer, the oxide, the contact material layer, the bottom electrode material layer, the phase change material layer, and the top electrode material layer.

FIG. 24A illustrates a top view of one embodiment of the substrate, the doped polysilicon layers, the word lines, a nitride layer, the oxide, a contact, a bottom electrode, a phase change element, and a bit line after etching.

FIG. 24B illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layers, the word lines, the nitride layer, the oxide, the contact, the phase change element, and the bit line after etching.

FIG. 24C illustrates another cross-sectional view of one embodiment of the substrate, the doped polysilicon layers, the word lines, the nitride layer, the oxide, the contact, the phase change element, and the bit line after etching.

FIG. 25A illustrates a top view of another embodiment of a substrate.

FIG. 25B illustrates a cross-sectional view of one embodiment of the substrate.

FIG. 25C illustrates another cross-sectional view of one embodiment of the substrate perpendicular to the view illustrated in FIG. 25B.

FIG. 26A illustrates a cross-sectional view of one embodiment of the substrate after doping.

FIG. 26B illustrates a cross-sectional view of one embodiment of the substrate after doping including optional co-implants.

FIG. 27 illustrates a cross-sectional view of one embodiment of the substrate, a doped polysilicon layer, a word line material layer, and a nitride layer.

FIG. 28 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layer, word lines, and the nitride layer after etching.

FIG. 29 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layer, the word lines, and an optional nitride layer.

FIG. 30 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layer, the word lines, the nitride layer, and a polysilicon layer.

FIG. 31 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layer, the word lines, the nitride layer, the polysilicon layer, and an oxide layer.

FIG. 32 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layer, the word lines, the nitride layer, the polysilicon layer, the oxide layer, and a mask layer.

FIG. 33 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layer, the word lines, the nitride layer, the polysilicon layer, and the oxide layer after etching a first opening.

FIG. 34 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layer, the word lines, the nitride layer, the polysilicon layer, and the oxide layer after etching a second opening.

FIG. 35 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layer, the word lines, the nitride layer, the polysilicon layer, and the oxide layer after oxidation.

FIG. 36 illustrates a cross-sectional view of one embodiment of the substrate, the doped polysilicon layer, the word lines, the nitride layer, the polysilicon layer, and oxide.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

It is to be understood that the features of the various exemplary embodiments described herein may be combined with each other, unless specifically noted otherwise.

FIG. 1 is a block diagram illustrating one embodiment of a system 90. System 90 includes a host 92 and a memory device 100. Host 92 is communicatively coupled to memory device 100 through communication link 94. Host 92 includes a microprocessor, computer (e.g., desktop, laptop, handheld), portable electronic device (e.g., cellular phone, personal digital assistant (PDA), MP3 player, video player, digital camera), or any other suitable device that uses memory. Memory device 100 provides memory for host 92. In one embodiment, memory device 100 provides embedded memory for host 92 and host 92 and memory device 100 are included on a single integrated circuit or circuit board. In one embodiment, memory device 100 includes a phase change memory device or other suitable resistive or resistivity changing material memory device.

FIG. 2 is a diagram illustrating one embodiment of memory device 100. Memory device 100 includes a write circuit 124, a controller 120, a memory array 102, and a sense circuit 126. Memory array 102 includes a plurality of resistive memory cells 104 a-104 d (collectively referred to as resistive memory cells 104), a plurality of bit lines (BLs) 112 a-112 b (collectively referred to as bit lines 112), and a plurality of word lines (WLs) 110 a-110 b (collectively referred to as word lines 110). In one embodiment, resistive memory cells 104 are phase change memory cells. In other embodiments, resistive memory cells 104 are another suitable type of resistive memory cells or resistivity changing memory cells.

Each memory cell 104 includes a phase change element 106 and a diode 108. Diodes 108 are U-shaped and formed in a silicon on insulator (SOI) substrate or local SOI structures between isolation regions. As used herein, the term “U-shaped” includes any substantially U, J, or backward J shape. In another embodiment, diodes 108 are replaced by bipolar transistors. The bipolar transistors are U-shaped and formed in a substrate having a common potential, such as ground. The bipolar transistors are formed between isolations regions such that one side of each bipolar transistor is coupled to common or ground. Therefore, the bipolar transistors function similarly to diodes. Diodes 108 are fabricated without selective epitaxy, which requires the use of an ultra-high vacuum chemical vapor deposition (UHV-CVD) tool to meet the temperature budget requirements.

As used herein, the term “electrically coupled” is not meant to mean that the elements must be directly coupled together and intervening elements may be provided between the “electrically coupled” elements.

Memory array 102 is electrically coupled to write circuit 124 through signal path 125, to controller 120 through signal path 121, and to sense circuit 126 through signal path 127. Controller 120 is electrically coupled to write circuit 124 through signal path 128 and to sense circuit 126 through signal path 130. Each phase change memory cell 104 is electrically coupled to a word line 110 and a bit line 112. Phase change memory cell 104 a is electrically coupled to bit line 112 a and word line 110 a, and phase change memory cell 104 b is electrically coupled to bit line 112 a and word line 110 b. Phase change memory cell 104 c is electrically coupled to bit line 112 b and word line 110 a, and phase change memory cell 104 d is electrically coupled to bit line 112 b and word line 110 b.

Each phase change memory cell 104 includes a phase change element 106 and a diode 108. Phase change memory cell 104 a includes phase change element 106 a and diode 108 a. One side of phase change element 106 a is electrically coupled to bit line 112 a, and the other side of phase change element 106 a is electrically coupled to one side of diode 108 a. The other side of diode 108 a is electrically coupled to word line 110 a. In another embodiment, the polarity of diode 108 a is reversed.

Phase change memory cell 104 b includes phase change element 106 b and diode 108 b. One side of phase change element 106 b is electrically coupled to bit line 112 a, and the other side of phase change element 106 b is electrically coupled to one side of diode 108 b. The other side of diode 108 b is electrically coupled to word line 110 b.

Phase change memory cell 104 c includes phase change element 106 c and diode 108 c. One side of phase change element 106 c is electrically coupled to bit line 112 b and the other side of phase change element 106 c is electrically coupled to one side of diode 108 c. The other side of diode 108 c is electrically coupled to word line 110 a.

Phase change memory cell 104 d includes phase change element 106 d and diode 108 d. One side of phase change element 106 d is electrically coupled to bit line 112 b and the other side of phase change element 106 d is electrically coupled to one side of diode 108 d. The other side of diode 108 d is electrically coupled to word line 110 b.

In another embodiment, each phase change element 106 is electrically coupled to a word line 110 and each diode 108 is electrically coupled to a bit line 112. For example, for phase change memory cell 104 a, one side of phase change element 106 a is electrically coupled to word line 110 a. The other side of phase change element 106 a is electrically coupled to one side of diode 108 a. The other side of diode 108 a is electrically coupled to bit line 112 a.

In one embodiment, each phase change element 106 comprises a phase change material that may be made up of a variety of materials. Generally, chalcogenide alloys that contain one or more elements from Group VI of the periodic table are useful as such materials. In one embodiment, the phase change material is made up of a chalcogenide compound material, such as GeSbTe, SbTe, GeTe, or AgInSbTe. In another embodiment, the phase change material is chalcogen free, such as GeSb, GaSb, InSb, or GeGaInSb. In other embodiments, the phase change material is made up of any suitable material including one or more of the elements Ge, Sb, Te, Ga, As, In, Se, and S.

Each phase change element 106 may be changed from an amorphous state to a crystalline state or from a crystalline state to an amorphous state under the influence of temperature change. The amount of crystalline material coexisting with amorphous material in the phase change material of one of the phase change elements thereby defines two or more states for storing data within memory device 100. In the amorphous state, a phase change material exhibits significantly higher resistivity than in the crystalline state. Therefore, the two or more states of the phase change elements differ in their electrical resistance. In one embodiment, the two or more states are two states and a binary system is used, wherein the two states are assigned bit values of “0” and “1”. In another embodiment, the two or more states are three states and a ternary system is used, wherein the three states are assigned bit values of “0”, “1”, and “2”. In another embodiment, the two or more states are four states that are assigned multi-bit values, such as “00”, “01”, “10”, and “11”. In other embodiments, the two or more states can be any suitable number of states in the phase change material of a phase change element.

Controller 120 includes a microprocessor, microcontroller, or other suitable logic circuitry for controlling the operation of memory device 100. Controller 120 controls read and write operations of memory device 100 including the application of control and data signals to memory array 102 through write circuit 124 and sense circuit 126. In one embodiment, write circuit 124 provides voltage pulses through signal path 125 and bit lines 112 to memory cells 104 to program the memory cells. In other embodiments, write circuit 124 provides current pulses through signal path 125 and bit lines 112 to memory cells 104 to program the memory cells.

Sense circuit 126 reads each of the two or more states of memory cells 104 through bit lines 112 and signal path 127. In one embodiment, to read the resistance of one of the memory cells 104, sense circuit 126 provides current that flows through one of the memory cells 104. Sense circuit 126 then reads the voltage across that one of the memory cells 104. In another embodiment, sense circuit 126 provides voltage across one of the memory cells 104 and reads the current that flows through that one of the memory cells 104. In another embodiment, write circuit 124 provides voltage across one of the memory cells 104 and sense circuit 126 reads the current that flows through that one of the memory cells 104. In another embodiment, write circuit 124 provides current that flows through one of the memory cells 104 and sense circuit 126 reads the voltage across that one of the memory cells 104.

In one embodiment, during a set operation of phase change memory cell 104 a, one or more set current or voltage pulses are selectively enabled by write circuit 124 and sent through bit line 112 a to phase change element 106 a, thereby heating phase change element 106 a above its crystallization temperature (but usually below its melting temperature). In this way, phase change element 106 a reaches its crystalline state or a partially crystalline and partially amorphous state during this set operation.

During a reset operation of phase change memory cell 104 a, a reset current or voltage pulse is selectively enabled by write circuit 124 and sent through bit line 112 a to phase change element 106 a. The reset current or voltage quickly heats phase change element 106 a above its melting temperature. After the current or voltage pulse is turned off, phase change element 106 a quickly quench cools into the amorphous state or a partially amorphous and partially crystalline state.

Phase change memory cells 104 b-104 d and other phase change memory cells 104 in memory array 102 are set and reset similarly to phase change memory cell 104 a using similar current or voltage pulses. In other embodiments, for other types of resistive memory cells, write circuit 124 provides suitable programming pulses to program the resistive memory cells 104 to the desired state.

FIG. 3 illustrates a cross-sectional view of one embodiment of a U-shaped diode access device 200. In one embodiment, a U-shaped diode access device 200 is used for each diode 108 previously described and illustrated with reference to FIG. 2. U-shaped diode access device 200 includes a silicon on insulator (SOI) substrate or local SOI structure 204, polysilicon layers or contacts 212 and 214, and contacts or lines 216 and 220. A diode is formed in substrate 204, which includes insulation material 202 and silicon regions 206, 208, and 210.

The diode includes a lightly doped (n−) region 206, a heavily doped (n+) region 208, and a heavily doped (p+) region 210. The top of n− doped region 206 contacts the bottom of n+ doped region 208 and the bottom of p+ doped region 210. In one embodiment, n+ doped region 208 is in the same horizontal plane as p+ doped region 210 and is isolated from p+ doped region 210 by dielectric material 218, thereby giving the diode a U-shape. In another embodiment, n+ doped region 208 is not in the same horizontal plane as p+ doped region 210, but n+ doped region 208 is still isolated from p+ doped region 210 by dielectric material 218, thereby maintaining the U-shape of the diode. In another embodiment, the polarity of the diode is reversed, such that region 206 is p− doped, region 208 is p+ doped, and region 210 is n+ doped.

The top of n+ doped region 208 contacts the bottom of n+ doped polysilicon layer 212. The top of n+ doped polysilicon layer 212 contacts the bottom of contact or line 216. The top of p+ doped region 210 contacts the bottom of p+ doped polysilicon layer 214. The top of p+ doped polysilicon layer 214 contacts the bottom of contact or line 220. The n+ doped polysilicon layer 212 is in the same horizontal plane as p+ doped polysilicon layer 214, and contact or line 216 is in the same horizontal plane as contact or line 220. The n+ doped polysilicon layer 212 and contact or line 216 are separated from p+ doped polysilicon layer 214 and contact or line 220 by dielectric material 218. In another embodiment, where the polarity of the diode is reversed, polysilicon layer 212 is p+ doped and polysilicon layer 214 is n+ doped.

In one embodiment, dielectric material 218 is self-aligned between contacts or lines 216 and 220. Insulation material 202 and dielectric material 218 includes SiO₂, SiO_(x), Si_(x)N_(y), fluorinated silica glass (FSG), boro-phosphorous silicate glass (BPSG), boro-silicate glass (BSG), or other suitable dielectric material. In one embodiment, contact or line 216 is a word line and contact or line 220 is a contact for coupling to a phase change element. Contacts or lines 216 and 220 include TiN, TaN, W, Al, Ti, Ta, TiSiN, TaSiN, TiAlN, TaAlN, Cu, WN, CoSi, NiSi, NiPtSi, WSi, a combination thereof, or other suitable electrically conductive material.

FIG. 4 illustrates a cross-sectional view of one embodiment of a bipolar transistor access device 230. In one embodiment, a U-shaped bipolar transistor access device 230 is used in place of each diode 108 previously described and illustrated with reference to FIG. 2. U-shaped bipolar transistor access device 230 includes a silicon substrate 232, polysilicon layers or contacts 212 and 214, and contacts or lines 216 and 220. A bipolar transistor is formed in substrate 232, which includes silicon regions 234, 206, 208, and 210.

The bipolar transistor includes a p doped region 234, an n− doped region 206, an n+ doped region 208, and a p+ doped region 210. In one embodiment, p doped region 234 is electrically coupled to common or ground such that the emitter-base path of the bipolar transistor acts as a diode. The top of p doped region 234 contacts the bottom of n− doped region 206. The top of n− doped region 206 contacts the bottom of n+ doped region 208 and the bottom of p+ doped region 210. In one embodiment, n+ doped region 208 is in the same horizontal plane as p+ doped region 210 and is isolated from p+ doped region 210 by dielectric material 218, thereby giving the bipolar transistor a U-shape. In another embodiment, n+ doped region 208 is not in the same horizontal plane as p+ doped region 210, but n+ doped region 208 is still isolated from p+ doped region 210 by dielectric material 218, thereby maintaining the U-shape of the bipolar transistor. In another embodiment, the polarity of the bipolar transistor is reversed, such that region 234 is n doped, region 206 is p− doped, region 208 is p+ doped, and region 210 is n+ doped.

The top of n+ doped region 208 contacts the bottom of n+ doped polysilicon layer 212. The top of n+ doped polysilicon layer 212 contacts the bottom of contact or line 216. The top of p+ doped region 210 contacts the bottom of p+ doped polysilicon layer 214. The top of p+ doped polysilicon layer 214 contacts the bottom of contact or line 220. The n+polysilicon layer 212 is in the same horizontal plane as p+ doped polysilicon layer 214, and contact or line 216 is in the same horizontal plane as contact or line 220. The n+ doped polysilicon layer 212 and contact or line 216 are separated from p+ doped polysilicon layer 214 and contact or line 220 by dielectric material 218. In another embodiment, where the polarity of the bipolar transistor is reversed, polysilicon layer 212 is p+ doped and polysilicon layer 214 is n+ doped.

In one embodiment, dielectric material 218 is self-aligned between contacts or lines 216 and 220. Dielectric material 218 includes SiO₂, SiO_(x), Si_(x)N_(y), FSG, BPSG, BSG, or other suitable dielectric material. In one embodiment, contact or line 216 is a word line and contact or line 220 is a contact for coupling to a phase change element. Contacts or lines 216 and 220 include TiN, TaN, W, Al, Ti, Ta, TiSiN, TaSiN, TiAlN, TaAlN, Cu, WN, CoSi, NiSi, NiPtSi, WSi, a combination thereof, or other suitable electrically conductive material.

FIG. 5 illustrates a cross-sectional view of one embodiment of an array 240 of diode access devices 200. In one embodiment, array 240 is used to provide diodes 108 of memory array 102 previously described and illustrated with reference to FIG. 2. Each diode access device 200 is similar to diode access device 200 previously described and illustrated with reference to FIG. 3. Each diode access device 200 includes dielectric material 218, which is self-aligned between each contact or line 216 and each contact or line 220 of each diode access device 200. Adjacent diode access devices 200 are isolated from each other by insulation material 242, which is processed separately. Insulation material 202 and 242 and dielectric material 218 include SiO₂, SiO_(x), Si_(x)N_(y), FSG, BPSG, BSG, or other suitable dielectric material.

FIG. 6 illustrates a cross-sectional view of another embodiment of an array 250 of diode access devices 200. In one embodiment, array 250 is used to provide diodes 108 of memory array 102 previously described and illustrated with reference to FIG. 2. Each diode access device 200 is similar to diode access device 200 previously described and illustrated with reference to FIG. 3. Each diode access device 200 includes dielectric material 218, which is self-aligned between each contact or line 216 and each contact or line 220 of each diode access device 200. Adjacent diode access devices 200 are isolated from each other by insulation material 252, which is self-aligned between a contact or line 216 of one diode access device 200 and a contact or line 220 of an adjacent diode access device 200. Insulation material 202 and 252 and dielectric material 218 include SiO₂, SiO_(x), Si_(x)N_(y), FSG, BPSG, BSG, or other suitable dielectric material.

FIG. 7 illustrates a cross-sectional view of one embodiment of an array 260 of bipolar transistor access devices 230. In one embodiment, array 260 is used to provide diodes 108 of memory array 102 previously described and illustrated with reference to FIG. 2. Each bipolar transistor access device 230 is similar to bipolar transistor access device 230 previously described and illustrated with reference to FIG. 4. Each bipolar transistor access device 230 includes dielectric material 218, which is self-aligned between each contact or line 216 and each contact or line 220 of each bipolar transistor access device 230. Adjacent bipolar transistor access devices 230 are isolated from each other by insulation material 262, which is processed separately. Insulation material 262 and dielectric material 218 include SiO₂, SiO_(x), Si_(x)N_(y), FSG, BPSG, BSG, or other suitable dielectric material.

FIG. 8 illustrates a cross-sectional view of another embodiment of an array 270 of bipolar transistor access devices 230. In one embodiment, array 270 is used to provide diodes 108 of memory array 102 previously described and illustrated with reference to FIG. 2. Each bipolar transistor access device 230 is similar to bipolar transistor access device 230 previously described and illustrated with reference to FIG. 4. Each bipolar transistor access device 230 includes dielectric material 218, which is self-aligned between each contact or line 216 and each contact or line 220 of each bipolar transistor access device 230. Adjacent bipolar transistor access devices 230 are isolated from each other by insulation material 272, which is self-aligned between a contact or line 216 of one bipolar transistor access device 230 and a contact or line 220 of an adjacent bipolar transistor access device 230. Insulation material 272 and dielectric material 218 include SiO₂, SiO_(x), Si_(x)N_(y), FSG, BPSG, BSG, or other suitable dielectric material.

The following FIGS. 9A-36 illustrate embodiments for a fabricating a phase change memory cell, such as a phase change memory cell 104 previously described and illustrated with reference to FIG. 2. Although the following FIGS. 9A-36 illustrate embodiments of a process for fabricating a phase change memory cell including a grounded bipolar transistor access device formed in a silicon substrate as previously described and illustrated with reference to FIG. 4, the illustrated process is also applicable to a phase change memory cell including a diode access device formed in a SOI structure or substrate as previously described and illustrated with reference to FIG. 3.

FIG. 9A illustrates a top view and FIGS. 9B and 9C illustrate cross-sectional views of one embodiment of a substrate 300. Substrate 300 includes insulation material 302 and an active area 304. In one embodiment, insulation material 302 includes isolation trenches and/or shallow trench isolation. Insulation material 302 laterally surrounds the top portion of active area 304. Insulation material 302 includes SiO₂, SiO_(x), Si_(x)N_(y), FSG, BPSG, BSG, or other suitable dielectric material.

FIG. 10A illustrates a cross-sectional view of one embodiment of substrate 300 after doping. Active area 304 of substrate 300 is doped to provide p doped region 234 and n− doped region 308. The top of p doped region 234 contacts the bottom of n− doped region 308. Insulation material 302 laterally surrounds n− doped region 308. Active area 304 is doped using ion implantation or another suitable technique.

FIG. 10B illustrates a cross-sectional view of one embodiment of substrate 300 after doping including optional co-implants 3 10. This optional embodiment is similar to the embodiment previously described and illustrated with reference to FIG. 10A, except that in this embodiment co-implants 310 are included for controlling doping diffusion. Co-implants 310 are implanted near the surface of n− doped region 308. Co-implants 310 include sulfur, carbon, or other suitable material. While the following FIGS. 11-24C illustrate substrate 300 without co-implants 310, substrate 300 with co-implants 310 may also be used.

FIG. 11 illustrates a cross-sectional view of one embodiment of substrate 300, a doped polysilicon layer 312 a, a word line material layer 314, and a nitride layer 316 a. An n+ doped polysilicon is deposited over substrate 300 to provide n+ doped polysilicon layer 312 a. Polysilicon layer 312 a is deposited using chemical vapor deposition (CVD), low pressure chemical vapor deposition (LPCVD), high density plasma-chemical vapor deposition (HDP-CVD), atomic layer deposition (ALD), metal organic chemical vapor deposition (MOCVD), physical vapor deposition (PVD), jet vapor deposition (JVD), or other suitable deposition technique.

An electrically conductive material, such as TiN, TaN, W, Al, Ti, Ta, TiSiN, TaSiN, TiAlN, TaAlN, Cu, WN, CoSi, NiSi, NiPtSi, WSi, a combination thereof, or other suitable word line material is deposited over n+ doped polysilicon layer 312 a to provide word line material layer 314. Word line material layer 314 is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. A nitride, such as Si_(x)N_(y) or another suitable dielectric material is deposited over word line material layer 314 to provide nitride layer 316 a. Nitride layer 316 a is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique.

FIG. 12 illustrates a cross-sectional view of one embodiment of substrate 300, doped polysilicon layer 312 b, word lines 216, and nitride layer 316 b after etching. Nitride layer 316 a, word line material layer 314, and n+ doped polysilicon layer 312 a are etched to provide opening or trench 318 and n+ doped polysilicon layer 312 b, word lines 216, and nitride layer 316 b. Trench 318 is defined using a suitable lithography process such that trench 318 is above a portion of n− doped region 308 and a portion of insulation material 302.

FIG. 13 illustrates a cross-sectional view of one embodiment of substrate 300, doped polysilicon layer 312 b, word lines 216, and an optional nitride layer 320. A nitride, such as Si_(x)N_(y) or another suitable dielectric material is deposited over exposed portions of nitride layer 316 b, word lines 216, and n+ doped polysilicon layer 312 b. The nitride layer is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. The nitride layer is then spacer etched to expose a portion of n+ doped polysilicon layer 312 b and to provide nitride layer 320, which includes nitride layer 316 b. Nitride layer 320 encapsulates word lines 216 to protect word lines 216 from oxidation during subsequent processing. In other embodiments, where a non-oxidizing material is used for word lines 216, word lines 216 are not encapsulated.

FIG. 14 illustrates a cross-sectional view of one embodiment of substrate 300, doped polysilicon layer 312 b, word lines 216, nitride layer 320, and a polysilicon layer 322. Polysilicon is deposited over exposed portions of nitride layer 320 and n+ doped polysilicon layer 312 b to provide polysilicon layer 322. Polysilicon layer 322 is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. In one embodiment, polysilicon layer 322 is in situ p doped or p doped using ion implantation. In another embodiment, polysilicon layer 322 is replaced with an amorphous silicon layer.

FIG. 15 illustrates a cross-sectional view of one embodiment of substrate 300, doped polysilicon layer 312 b, word lines 216, nitride layer 320, polysilicon layer 322, and an oxide layer 324. An oxide, such as SiO₂ or other suitable oxide is deposited over polysilicon layer 322 to provide an oxide layer. The oxide layer is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. The oxide layer is then back-etched to provide oxide layer 324 and to expose portions of polysilicon layer 322.

FIG. 16 illustrates a cross-sectional view of one embodiment of substrate 300, doped polysilicon layer 212, word lines 216, nitride layer 320, a polysilicon layer 330, and oxide layer 324 after etching. The exposed portions of polysilicon layer 322 and the underlying portions of n+ doped polysilicon layer 312 b are selectively etched to expose nitride layer 320, a portion of n− doped region 308, and a portion of insulation material 302. The etching provides n+ doped polysilicon layer 212 and polysilicon layer 330, which includes portions of n+ doped polysilicon layer 312 b and polysilicon layer 322. The exposed portion of n− doped region 308 is etched to provide opening or trench 326. The exposed portion of insulation material 302 is etched to provide opening or trench 328. In one embodiment, the depth of opening 326 is greater than the depth of opening 328.

FIG. 17 illustrates a cross-sectional view of one embodiment of substrate 300, doped polysilicon layer 212, word lines 216, nitride layer 320, polysilicon layer 330, and oxide layer 324 after oxidation. The exposed portions of polysilicon layers 212 and 330 and the exposed portions of n− doped region 308 are oxidized to provide oxide 334. In one embodiment, where word lines 216 are not encapsulated by nitride layer 320, the exposed portions of polysilicon layers 212 and 330 and the exposed portions of n− doped region 308 are selectively oxidized to provide oxide 334.

FIG. 18 illustrates a cross-sectional view of one embodiment of substrate 300, doped polysilicon layer 212, word lines 216, nitride layer 320, polysilicon layer 330, and oxide 336. In one embodiment, a nitride is used in place of oxide 336. An oxide or nitride, such as SiO₂, Si_(x)N_(y), or other suitable dielectric material is deposited over nitride layer 320, oxide layer 324, and oxide 324 to provide an oxide or nitride layer. The oxide or nitride layer is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. The oxide or nitride layer and oxide layer 324 are then back-etched to provide oxide 336 and to expose nitride layer 320 and polysilicon layer 330.

FIG. 19 illustrates a cross-sectional view of one embodiment of substrate 300, doped polysilicon layer 212, word lines 216, nitride layer 320, oxide 336, and a doped polysilicon layer 214 a. In one embodiment, polysilicon layer 330 is doped and/or counter doped to provide p+ doped polysilicon layer 214 a. In another embodiment, polysilicon layer 330 is back-etched and a p+ doped polysilicon layer is then deposited to provide p+ doped polysilicon layer 214 a. In another embodiment, polysilicon layer 330 is back-etched and an undoped polysilicon layer is then deposited. The undoped polysilicon layer is then doped using ion implantation or another suitable technique to provide p+ doped polysilicon layer 214 a.

FIG. 20 illustrates a cross-sectional view of one embodiment of substrate 232, doped polysilicon layers 212 and 214 a, word lines 216, nitride layer 320, and oxide 336 after annealing. Substrate 300 and doped polysilicon layers 212 and 214 a are annealed to provide substrate 232. During annealing, dopants from n+ doped polysilicon layer 212 diffuse into the underlying n− doped region 308 and dopants from p+ doped polysilicon layer 214 a diffuse into the underlying n− doped region 308. The diffusion of dopants from n+ doped polysilicon layer 212 into n− doped region 308 provides n+ doped region 208. The diffusion of dopants from p+ doped polysilicon layer 214 a into n− doped region 308 provides p+ doped region 210. The bottom of n+ doped region 208 and the bottom of p+ doped region 210 contact the top of n− doped region 206. The n+ doped region 208 is in the same horizontal plane as p+ doped region 210 and is separated from p+ doped region 210 by oxide 336. Therefore, a U-shaped bipolar transistor is formed in substrate 232.

FIG. 21 illustrates a cross-sectional view of one embodiment of substrate 232, doped polysilicon layers 212 and 214 a, word lines 216, nitride layer 320, oxide 336, and a contact material layer 338 a. An electrically conductive material, such as TiN, TaN, W, Al, Ti, Ta, TiSiN, TaSiN, TiAlN, TaAlN, Cu, WN, CoSi, NiSi, NiPtSi, WSi, a combination thereof, or other suitable contact material is deposited over exposed portions of nitride layer 320, oxide 336, and p+ doped polysilicon layer 214 a to provide a contact material layer. The contact material layer is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. The contact material layer is then planarized to expose nitride layer 320 and to provide contact material layer 338 a. The contact material layer is planarized using chemical mechanical planarization (CMP) or another suitable planarization technique.

FIG. 22 illustrates a cross-sectional view of one embodiment of substrate 232, doped polysilicon layers 212 and 214 a, word lines 216, a nitride layer 342 a, oxide 336, a contact material layer 338 b, and a bottom electrode material layer 340 a. Contact material layer 338 a is recess etched to provide contact material layer 338 b. A nitride, such as Si_(x)N_(y) or other suitable dielectric material is deposited over nitride layer 320 and contact material layer 338 b to provide a nitride layer. The nitride layer is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. The nitride layer is then spacer etched to expose a portion of contact material layer 338 b and to provide nitride layer 342 a, which includes nitride layer 320.

An electrically conductive material, such as TiN, TaN, W, Al, Ti, Ta, TiSiN, TaSiN, TiAlN, TaAlN, Cu, WN, CoSi, NiSi, NiPtSi, WSi, a combination thereof, or other suitable electrode material is deposited over exposed portions of nitride layer 342 a and contact material layer 338 b to provide an electrode material layer. The electrode material layer is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. The electrode material layer is then planarized to expose nitride layer 342 a and to provide bottom electrode material layer 340 a. The electrode material layer is planarized using CMP or another suitable planarization technique. In one embodiment, bottom electrode material layer 340 a has tapered sidewalls. In other embodiments, bottom electrode material layer 340 a has another suitable shape.

FIG. 23A illustrates a cross-sectional view of one embodiment of substrate 232, doped polysilicon layers 212 and 214 a, word lines 216, a nitride layer 342 b, oxide 336, contact material layer 338 b, bottom electrode material layer 340 a, a phase change material layer 344 a, and a top electrode material layer 346 a. FIG. 23B illustrates another cross-sectional view through n+ doped polysilicon layer 212 and perpendicular to the view illustrated in FIG. 23A. FIG. 23C illustrates another cross-sectional view through p+ doped polysilicon layer 214 a and perpendicular to the view illustrated in FIG. 23A.

A nitride, such as Si_(x)N_(y) or other suitable dielectric material is deposited over nitride layer 342 a and electrode material layer 340 a to provide a nitride layer. The nitride layer is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. The nitride layer is then etched to form a trench exposing a portion of electrode material layer 340 a and to provide nitride layer 342 b, which includes nitride layer 342 a.

A phase change material, such as a chalcogenide compound material or other suitable phase change material is deposited over exposed portions of nitride layer 342 b and bottom electrode material layer 340 a to provide phase change material layer 344 a. Phase change material layer 344 a is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. An electrically conductive material, such as TiN, TaN, W, Al, Ti, Ta, TiSiN, TaSiN, TiAlN, TaAlN, Cu, WN, CoSi, NiSi, NiPtSi, WSi, a combination thereof, or other suitable electrode material is deposited over phase change material layer 344 a to provide top electrode material layer 346 a. Top electrode material layer 346 a is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique.

FIG. 24A illustrates a top view and FIGS. 24B and 24C illustrate cross-sectional views of one embodiment of substrate 232, doped polysilicon layers 212 and 214, word lines 216, nitride layer 342, oxide 336, a contact 220, a bottom electrode 340, a phase change element 344, and a bit line 346 after etching. Top electrode material layer 346 a, phase change material layer 344 a, nitride layer 342 b, bottom electrode material layer 340 a, contact material layer 338 b, and p+ doped polysilicon layer 214 a are etched to expose insulation material 302 and to provide p+ doped polysilicon layer 214, contact 220, bottom electrode 340, nitride layer 342, phase change element 344, and bit line 346. In this way, p+ doped polysilicon layer 214, contact 220, bottom electrode 340, and phase change element 244 are self-aligned to bit line 346.

Insulation material, such SiO₂, SiO_(x), Si_(x)N_(y), FSG, BPSG, BSG, or other suitable dielectric material is deposited over exposed portions of insulation material 302, p+ doped polysilicon layer 214, contact 220, bottom electrode 340, nitride layer 342, phase change element 344, and bit line 346 to provide an insulation material layer (not shown). The insulation material layer is then planarized to expose bit line 346. The insulation material layer is planarized using CMP or another suitable planarization technique. In other embodiments, bottom electrode 340, nitride layer 342, and phase change element 344 are fabricated to provide any suitably shaped bottom electrode 340 and phase change element 344.

The following FIGS. 25A-36 illustrate another embodiment for fabricating a phase change memory cell, such as a phase change memory cell 104 previously described and illustrated with reference to FIG. 2.

FIG. 25A illustrates a top view and FIGS. 25B and 25C illustrate cross-sectional views of another embodiment of a substrate 400. Substrate 400 includes insulation material 402 and an active area 404. In one embodiment, insulation material 402 includes isolation trenches. Active area 404 is between insulation material 402. Insulation material 402 includes SiO₂, SiO_(x), Si_(x)N_(y), FSG, BPSG, BSG, or other suitable dielectric material.

FIG. 26A illustrates a cross-sectional view of one embodiment of substrate 400 after doping. Active area 404 of substrate 400 is doped to provide p doped region 234 and n− doped region 408. The top of p doped region 234 contacts the bottom of n− doped region 408. Active area 404 is doped using ion implantation or another suitable technique.

FIG. 26B illustrates a cross-sectional view of one embodiment of substrate 400 after doping including optional co-implants 410. This optional embodiment is similar to the embodiment previously described and illustrated with reference to FIG. 26A, except that in this embodiment co-implants 410 are included for controlling doping diffusion. Co-implants 410 are implanted near the surface of n− doped region 408. Co-implants 410 include sulfur, carbon, or other suitable material. While the following FIGS. 27-36 illustrate substrate 400 without co-implants 410, substrate 400 with co-implants 410 may also be used.

FIG. 27 illustrates a cross-sectional view of one embodiment of substrate 400, a doped polysilicon layer 312 a, a word line material layer 314, and a nitride layer 316 a. An n+ doped polysilicon is deposited over substrate 400 to provide n+ doped polysilicon layer 312 a. Polysilicon layer 312 a is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique.

An electrically conductive material, such as TiN, TaN, W, Al, Ti, Ta, TiSiN, TaSiN, TiAlN, TaAlN, Cu, WN, CoSi, NiSi, NiPtSi, WSi, a combination thereof, or other suitable word line material is deposited over n+ doped polysilicon layer 312 a to provide word line material layer 314. Word line material layer 314 is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. A nitride, such as Si_(x)N_(y) or another suitable dielectric material is deposited over word line material layer 314 to provide nitride layer 316 a. Nitride layer 316 a is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique.

FIG. 28 illustrates a cross-sectional view of one embodiment of substrate 400, doped polysilicon layer 312 b, word lines 216, and nitride layer 316 b after etching. Nitride layer 316 a, word line material layer 314, and n+ doped polysilicon layer 312 a are etched to provide opening or trench 318 and n+ doped polysilicon layer 312 b, word lines 216, and nitride layer 316 b. Trench 318 is defined using a suitable lithography process.

FIG. 29 illustrates a cross-sectional view of one embodiment of substrate 400, doped polysilicon layer 312 b, word lines 216, and an optional nitride layer 320. A nitride, such as Si_(x)N_(y) or another suitable dielectric material is deposited over exposed portions of nitride layer 316 b, word lines 216, and n+ doped polysilicon layer 312 b. The nitride layer is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. The nitride layer is then spacer etched to expose a portion of n+ doped polysilicon layer 312 b and to provide nitride layer 320, which includes nitride layer 316 b. Nitride layer 320 encapsulates word lines 216 to protect word lines 216 from oxidation during subsequent processing. In other embodiments, where a non-oxidizing material is used for word lines 216, word lines 216 are not encapsulated.

FIG. 30 illustrates a cross-sectional view of one embodiment of substrate 400, doped polysilicon layer 312 b, word lines 216, nitride layer 320, and a polysilicon layer 322. Polysilicon is deposited over exposed portions of nitride layer 320 and n+ doped polysilicon layer 312 b to provide polysilicon layer 322. Polysilicon layer 322 is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. In one embodiment, polysilicon layer 322 is in situ p doped or p doped using ion implantation.

FIG. 31 illustrates a cross-sectional view of one embodiment of substrate 400, doped polysilicon layer 312 b, word lines 216, nitride layer 320, polysilicon layer 322, and an oxide layer 324. An oxide, such as SiO₂ or other suitable oxide is deposited over polysilicon layer 322 to provide an oxide layer. The oxide layer is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. The oxide layer is then back-etched to provide oxide layer 324 and to expose portions of polysilicon layer 322.

FIG. 32 illustrates a cross-sectional view of one embodiment of substrate 400, doped polysilicon layer 312 b, word lines 216, nitride layer 320, polysilicon layer 322, oxide layer 324, and a mask layer 410. Mask layer 410, such as a hardmask or other suitable mask is formed over a portion of polysilicon layer 322 and oxide layer 324.

FIG. 33 illustrates a cross-sectional view of one embodiment of substrate 400, doped polysilicon layer 312 c, word lines 216, nitride layer 320, a polysilicon layer 412, and oxide layer 324 after etching a first opening 414 a. The exposed portions of polysilicon layer 322 are selectively etched to provide polysilicon layer 412 and to expose portions of nitride layer 320 and portions of n+ doped polysilicon layer 312 b. The exposed portions of n+ doped polysilicon layer 312 b are then etched to provide n+polysilicon layer 312 c and to expose a portion of active area 404 of substrate 400. The exposed portion of active area 404 of substrate 400 is etched to provide first opening or trench 414 a. Mask layer 410 is then removed.

FIG. 34 illustrates a cross-sectional view of one embodiment of substrate 400, doped polysilicon layer 212, word lines 216, nitride layer 320, polysilicon layer 330, and oxide layer 324 after etching a second opening 416. The exposed portions of polysilicon layer 412 and the underlying portion of n+doped polysilicon layer 312 c are selectively etched to expose nitride layer 320 and a portion of active area 404 of substrate 400. The etching provides n+ doped polysilicon layer 212 and polysilicon layer 330, which includes portions of n+doped polysilicon layer 312 c and polysilicon layer 412. The exposed portion of active area 404 of substrate 400 is etched to provide second opening or trench 416 and to expand first opening 414 a to provide first opening 414. In one embodiment, the depth of second opening 416 is less than the depth of first opening 414.

FIG. 35 illustrates a cross-sectional view of one embodiment of substrate 400, doped polysilicon layer 212, word lines 216, nitride layer 320, polysilicon layer 330, and oxide layer 324 after oxidation. The exposed portions of polysilicon layers 212 and 330 and the exposed portions of active area 404 of substrate 400 are oxidized to provide oxide 418. In one embodiment, where word lines 216 are not encapsulated by nitride layer 320, the exposed portions of polysilicon layers 212 and 330 and the exposed portions of active area 404 of substrate 400 are selectively oxidized to provide oxide 418.

FIG. 36 illustrates a cross-sectional view of one embodiment of substrate 400, doped polysilicon layer 212, word lines 216, nitride layer 320, polysilicon layer 330, and oxide 336. In one embodiment, a nitride is used in place of oxide 336. An oxide or nitride, such as SiO₂, Si_(x)N_(y), or other suitable dielectric material is deposited over nitride layer 320, oxide layer 324, and oxide 418 to provide an oxide or nitride layer. The oxide or nitride layer is deposited using CVD, LPCVD, HDP-CVD, ALD, MOCVD, PVD, JVD, or other suitable deposition technique. The oxide or nitride layer and oxide layer 324 are then back-etched to provide oxide 336 and to expose nitride layer 320 and polysilicon layer 330. A process similar to the process previously described and illustrated with reference to FIGS. 19-24C is then performed to complete the fabrication of the phase change memory cell.

Embodiments provide U-shaped diodes or bipolar transistors for accessing resistive memory cells. Contact to the U-shaped diodes or bipolar transistors is made from the top of the access devices through polysilicon layers, which provide large metal to silicon transition areas. An array of the U-shaped access devices does not include buried metal lines thereby avoiding large series resistances. In addition, the self-alignment of the memory cells reduces area consumption to provide smaller memory cells compared to typical memory cells.

While the specific embodiments described herein substantially focused on using phase change memory elements, the embodiments can be applied to any suitable type of resistive or resistivity changing memory elements.

Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof. 

1. An integrated circuit comprising: a first contact; a second contact; a U-shaped access device coupled to the first contact and the second contact; and self-aligned dielectric material isolating the first contact from the second contact.
 2. The integrated circuit of claim 1, wherein the access device is provided in a substrate, the access device comprising: a doped first region having a first polarity; a doped second region having a second polarity opposite the first polarity, the second region isolated from the first region by the dielectric material; and a doped third region having the first polarity, the third region contacting the first region and the second region.
 3. The integrated circuit of claim 2, wherein the substrate includes a doped fourth region having the second polarity, the fourth region contacting the third region.
 4. The integrated circuit of claim 2, wherein the substrate comprises a silicon on insulator structure including an insulating material layer, the insulating material layer contacting the third region.
 5. The integrated circuit of claim 1, wherein the access device comprises one of a diode and a bipolar transistor.
 6. The integrated circuit of claim 1, further comprising: a resistive memory element coupled to the first contact; a first line coupled to the memory element; and a second line coupled to the second contact.
 7. The integrated circuit of claim 6, wherein the memory element is self-aligned to the first line.
 8. The integrated circuit of claim 6, wherein the first contact comprises a first silicon layer coupling a first side of the access device to the memory element, and wherein the second contact comprises a second silicon layer coupling a second side of the access device to the second line.
 9. The integrated circuit of claim 6, wherein the memory element comprises a phase change element.
 10. A system comprising: a host; and a memory device communicatively coupled to the host, the memory device comprising: a U-shaped access device; and a resistance changing memory element coupled to a first side of the access device.
 11. The system of claim 10, wherein the access device is provided in a substrate, the access device comprising: a heavily doped first region having a first polarity; a heavily doped second region having a second polarity opposite the first polarity, the second region isolated from the first region; and a lightly doped third region having the second polarity, the third region contacting the first region and the second region.
 12. The system of claim 10, wherein the access device comprises one of a diode and a bipolar transistor.
 13. The system of claim 10, wherein the memory device further comprises: a first line coupled to the memory element; and a second line coupled to a second side of the access device.
 14. The system of claim 13, wherein the memory element is self-aligned to the second line.
 15. The system of claim 10, wherein the memory element comprises a phase change element.
 16. A method for fabricating an integrated circuit, the method comprising: fabricating a U-shaped access device in a substrate; and fabricating a resistance changing memory element coupled to a first side of the access device.
 17. The method of claim 16, wherein fabricating the access device comprises: lightly doping a first region of the substrate to have a first polarity; heavily doping a second region of the substrate to have the first polarity, a bottom of the second region contacting a top of the first region; heavily doping a third region of the substrate to have a second polarity opposite the first polarity, a bottom of the third region contacting the top of the first region; and isolating the second region from the third region.
 18. The method of claim 16, wherein fabricating the access device comprises fabricating a diode in a silicon on insulator structure.
 19. The method of claim 16, wherein fabricating the access device comprises fabricating a bipolar transistor in a silicon substrate.
 20. The method of claim 16, further comprising: fabricating a first line coupled to the memory element; and fabricating a second line coupled to a second side of the access device.
 21. The method of claim 16, wherein fabricating the access device comprises: providing the substrate including an active area and isolation regions, the active area including a first region having a first polarity; depositing a doped first silicon layer over the substrate, the first silicon layer having the first polarity; depositing an electrically conductive material layer over the first silicon layer; depositing a nitride layer over the electrically conductive material layer; etching a portion of the nitride layer and the electrically conductive material layer to provide an opening exposing a portion of the first silicon layer; depositing a second silicon layer over exposed portions of the first silicon layer, the electrically conductive material layer, and the nitride layer; depositing an oxide layer over the second silicon layer in the opening; etching exposed portions of the second silicon layer and underlying portions of the first silicon layer and the substrate to provide a first trench having a first depth and a second trench having a second depth less than the first depth; filling the first trench and the second trench with a dielectric material; removing the oxide layer to expose the second silicon layer; doping the second silicon layer to have a second polarity opposite the first polarity; and annealing the first and second silicon layers to diffuse dopants into a portion of the first region to provide the access device.
 22. The method of claim 21, further comprising: oxidizing exposed portions of the first silicon layer, the second silicon layer, and the active area after etching to provide the first and second trenches.
 23. The method of claim 16, wherein fabricating the access device comprises: providing the substrate including an active area and isolation regions, the active area including a doped first region having a first polarity; depositing a doped first silicon layer over the substrate, the first silicon layer having the first polarity; depositing an electrically conductive material layer over the first silicon layer; depositing a nitride layer over the electrically conductive material layer; etching a portion of the nitride layer and the electrically conductive material layer to provide an opening exposing a portion of the first silicon layer; depositing a second silicon layer over exposed portions of the first silicon layer, the electrically conductive material layer, and the nitride layer; depositing an oxide layer over the second silicon layer in the opening; masking a portion of the oxide layer and the second silicon layer; etching exposed portions of the second silicon layer and underlying portions of the first silicon layer and the substrate to provide a first trench having a first depth; removing the mask; etching exposed portions of the second silicon layer and underlying portions of the first silicon layer and the substrate to provide a second trench having a second depth less than the first depth; filling the first trench and the second trench with a dielectric material; removing the oxide layer to expose the second silicon layer; doping the second silicon layer to have a second polarity opposite the first polarity; and annealing the first and second silicon layers to diffuse dopants into a portion of the first region to provide the access device.
 24. The method of claim 23, further comprising: oxidizing exposed portions of the first silicon layer, the second silicon layer, and the active area after etching to provide the second trench.
 25. The method of claim 16, wherein fabricating the resistance changing memory element comprises fabricating a phase change element. 